1. Field of the Invention
This invention relates to an aperture grill supporting frame and a method for manufacturing thereof, more particularly to an aperture grill supporting frame which is used for an in-line cathode ray tube to support an aperture grill with a grid of longitudinal slits.
2. Prior Art
To take an example, the television receiver incorporates a cathode ray tube. As such cathode ray tube, the in-line cathode ray tube is well known in which three electron beams are arranged to be in-line, namely, arranged to form a row in a horizontal direction.
This in-line cathode ray tube is provided with a three-beam electron gun based on unit electron guns to emit three electron beams which are arranged in a horizontal line, a convergence electrode to converge the electron beams emitted from the electron gun, a deflecting yoke to deflect the electron beams, a color sorting mechanism having an aperture grill with a grid of longitudinal slits, and a glass bulb which has a phosphor screen which has its surface coated in longitudinal parallel lines with phosphors giving red, green and blue lights.
With this cathode ray tube, the electron beams emitted from the electron gun, after having been converged by the convergence electrode, are deflected by the deflecting yoke in horizontal and vertical directions in synchrony with horizontal and vertical synchronization signals, and are scanned over the whole surface of the phosphor screen.
The electron beams which have been deflected by the deflecting yoke have their unnecessary portion masked by the color sorting mechanism. Namely, the color sorting mechanism passes only the fraction of electron beams which have been designed to be directed onto the phosphor screen. The electron beams having passed the color sorting mechanism properly strike against red, blue and green phosphors, causing them to illuminate to display a color image on the screen.
The color sorting mechanism consists of an aperture grill with a grid of longitudinal slits, an aperture grill supporting frame which supports the aperture grill by stretching it in a horizontal direction, damper wires which are placed in contact with thin tapes constituting the aperture grill to give them axially acting forces, and damper springs which stretch both ends of damper wires.
FIG. 1 illustrates the aperture grill supporting frame 42 and aperture grill 41. FIG. 1A gives a frontal view of the aperture grill supporting frame 42 and aperture grill 41, FIG. 1B a lateral view of the aperture grill supporting frame 42, and FIG. 1C a bottom view of the aperture grill supporting frame 42 and aperture grill 41.
The aperture grill 41 is produced after a rolled plate material has been subject to photoetching to produce slits in the form of a grid of longitudinal lines, and parts between adjacent slits are occupied by thin tapes. Namely, the aperture grill 41 takes the form of an assembly of thin tapes. As will be described later, this aperture grill 41 is welded, while being kept stretched in a vertical direction or in a Y-axis direction, to the aperture grill supporting frame 42. The damper wires are made of, for example, tungsten wire, and are placed such that their direction is normal to the long axes of the slits of the aperture grill 41. Both ends of these damper wires are stretched by damper springs mounted to the aperture grill supporting frame 42. By virtue of the tension from the damper springs, the damper wires are placed in contact with individual thin tapes constituting the aperture grill 41 to give a vertically acting force to each of the thin tapes. Thus, the damper wire prevents the thin tapes of aperture grill 41 from being put into vibration by, for example, a certain external vibrating source, through the friction generated by their contact with individual thin tapes. Namely, the damper wires exert a uniformly acting anti-vibration effect on the whole surface of the aperture grill 41 by giving uniformly acting forces on individual thin tapes of the aperture grill 41.
The aperture grill supporting frame 42 consists of upper and lower frames 45 and 46 which together support the aperture grill 41 by stretching it in a horizontal direction, and side frames 47 and 48 which are connected to the upper and lower frames 45 and 46 at their ends. The upper and lower frames 45 and 46 have a cross-section in the form of an inverted L as shown in FIG. 1B, and are generally shaped as a rod.
The surfaces 45a and 46a (to be referred to as surfaces for welding hereinafter) of upper and lower frames 45 and 46 of aperture grill supporting frame 42, through which the aperture grill 41 is welded to the supporting frame, have been so processed as to give a part of a columnar wall surface with a radius of R as is seen from FIG. 1C, and FIG. 2A which gives an enlarged view of part A of FIG. 1C. Then, for example, on respective four points of the upper and lower frames 45 and 46 are applied pressures from a pressurizing mechanism 51 in the directions as indicated by arrows a and b of FIG. 1A so that the interval between the two frames may be reduced.
As a result, not only the upper frame 45 undergoes an elastic deformation in -Y direction as represented by the interrupted lines of FIG. 1A, but also the surfaces for welding 45a at its both ends experience elastic deformations in -Z direction with respect to the center of the frame, for example, as represented by the interrupted lines of FIG. 1C. Further, not only the lower frame 46 undergoes an elastic deformation in +Y direction as represented by the interrupted lines of FIG. 1A, but also the surfaces for welding 46a at its both ends experience elastic deformations in -Z direction with respect to the center of the frame, for example, as represented by the dotted lines of FIG. 1C. On the other hand, the side frame 47 undergoes an elastic deformation in +X and -Z directions as indicated by the interrupted lines of FIGS. 1A and 1B while the side frame 48 undergoes an elastic deformation in -X and -Z directions as indicated by the interrupted lines of FIGS. 1A and 1B. The aperture grill 41 is welded to the surfaces 45a and 46a for welding of the upper and lower frames 45 and 46 of aperture grill supporting frame 42 whose frames have been subject to such deformations as described above, and, after welding, the pressure from the pressurizing mechanism is released. As a result, the frames constituting the aperture grill supporting frame 42, being relieved of pressures which force them to undergo elastic deformations, try to return to original states through their intrinsic elasticity, and this action gives a tension to stretch the aperture grill 41 in Y-axis direction, or in a vertical direction, and hence the aperture grill 41 becomes a tautly stretched mask.
On this tautly stretched aperture grill 41 is placed a damper wire 43 as indicated by FIG. 2B to intersect the long axis of a slit at right angles, and its both ends are stretched by damper springs 44 fastened thereto. Here, the aperture grill 41 is welded to the upper and lower frames 45 and 46, while the latter are subject to elastic deformations, and, because these welded surfaces 45a and 46a with a form corespondent with a part of a columnar wall surface with a radius of R as described earlier are assembled as initially designed, the welded surfaces 45a and 46a being subject to elastic deformations do not actually give that designed form. Accordingly, forces N acting on the thin tapes constituting the aperture grill 41 are not uniform. Particularly at places where a gap c develops between the damper wire 43 and aperture grill 41, the force N pressing the aperture grill 41 in an axial direction is weakened or lost. Hence, frictional forces acting between the thin tapes and damper wires 43 will not become uniform, and not be able to give an anti-vibration effect uniformly over the whole surface of the aperture grill 41.
FIG. 3 gives a comparison of the surface shapes of the surfaces for welding surfaces 45a and 46a of upper and lower frames 45 and 46 before the aperture grill 41 is welded to them, and those of the same surfaces for welding 45a and 46a after welding. The surfaces for welding 45a and 46a before the aperture grill 41 is welded to them have the same shape with a part of a columnar wall surface with a radius of R, and the same surfaces 45a and 46a after the aperture grill 41 has been welded to them give a sector with a radius of R which has an indentation at each end.
Assume that the direction which the long sides of the aperture grill 41 supported by the pair of upper and lower frames 45 and 46 take is in an X-axis direction, the direction which the short sides of the aperture grill 41 take and is normal to X-axis direction is in a Y-axis direction, and the direction towards which an electron beam is discharged from the electron gun and is normal to X-axis and Y-axis directions is in a Z-axis direction.